Hitherto, an extruded styrene resin foam has widely been used as a thermal insulating material for building due to its suitable workability and thermal insulating characteristics. In order to obtain an extruded styrene resin foam with excellent thermal insulating characteristics, techniques using flons represented by flon 142b and flon 134a have been proposed in many past prior patents. So far, a technique using flon 142b has been fixed in the field concerned.
However, recently, the ozone layer problem and global warming problem have been attracting attention and flons are desired to be replaced if possible.
Further, halogenated hydrocarbons such as methyl chloride, ethyl chloride and the like have been commonly used as a suitable blowing agent in relation to plasticizing effect, solubility and foaming property against a resin. However, these blowing agents are substances obliged to keep work environmental preservation in production plants or the like from the viewpoint of industrial hygienic environments and such blowing agents are desired to be replaced with other blowing agents.
In such situation, it has been investigated to substitute a blowing agent excellent in the environmental compatibility as the blowing agent to be employed for an extruded styrene resin foam. Naturally, together with the replacement of the blowing agent, it has also been investigated to achieve physical properties such as thermal insulating property, flame retardant property, and mechanical strength required for the thermal insulating material for construction.
As an extruded styrene resin foam using a blowing agent other than flons and its production method, an extruded styrene resin foam and its production method using propane, butane or a mixture thereof, or these hydrocarbons with methyl chloride, ethyl chloride or a mixture thereof as a blowing agent are disclosed in JP 10-237210 A. However, in the case that a blowing agent composed of propane or butane, which has poor plasticizing effect against polystyrene resin, mixed at a high ratio is used to obtain a foam with a low density, a phenomenon of insufficient gas dispersion takes place frequently to make it impossible to stably obtain satisfactory foams. Further, as a means of suppressing this phenomenon, a special kneading/mixing apparatus such as a pin mixer or the like has to be employed to obtain such foams.
Also, in the same official gazette, it is disclosed that hexabromocyclododecane or tetrabromobisphenol A is used in an amount of 1 to 3% by weight and the amounts of propane and butane as a blowing agent remaining in the resultant foam are adjusted to be not more than 3.5% by weight and not more than 2.0% by weight, respectively, in order to satisfy the flame retardant property prescribed in JIS A 9511. Accordingly, there is a description of the upper limit of the amount of propane, butane or their mixture used. However, in that case, if the mixing ratio of methyl chloride, ethyl chloride, or their mixture is that as described in the official gazette, the foaming energy is insufficient and it is very difficult to actually obtain a foam with a low density. Further, as a blowing agent, a halogenated hydrocarbon such as methyl chloride, ethyl chloride or the like is used and this restricts the work environments for production of foams.
Further, in the case of the foam using no flons as described in the foregoing official gazette, in order to adjust the remaining gas amount of propane or butane to the aforesaid level, it is required to restrict the amount of propane or butane added when producing a foam, or it is required to store the foam for a long time until the blowing agent is decreased after the production of the foam, which causes problems such as poor production stability in extrusion foaming and poor productivity.
Moreover, with the amount of propane or butane in the foam using no flons as described in the foregoing official gazette, it is very difficult to obtain a foam having high-level thermal insulating property, for example, as required for the extrusion method polystyrene foam thermal insulating board Class 3a or 3b as prescribed JIS A 9511. In order to obtain a foam having high-level thermal insulating property, it is supposed to allow a saturated hydrocarbon compound such as propane or butane to remain in a larger amount. For example, according to the present inventors' investigations, although it depends on the foam density, in the case that the foam density is within a range of 20 to 40 kg/m3, it is preferable for propane to remain in an amount of 4% by weight or more and for butanes to remain in an amount of 2.5% by weight or more, particularly in an amount of 3% by weight or more, based on the foam weight. However, in the case where compounds with a relatively high combustibility like aliphatic hydrocarbons represented by propane and butane are allowed to remain in large amounts, it sometimes takes place that the flame retardant property prescribed in JIS A 9511 cannot be satisfied only by incorporating hexabromocyclodedecane or tetrabromobisphenol A in an amount of 1 to 3% by weight as described in the foregoing official gazette. On the contrary, in order to improve the flame retardant property, it is supposed to increase the amount of a flame retardant to be added, however a stable flame retardant property cannot be obtained only by increasing the content thereof. Also, although the styrene resin, which is a basic material of a foam, itself is made flame-retardant, hydrocarbons to be evaporated from the foam upon burning are easy to be ignited and the tendency that it is difficult to suppress combustion is still difficult to be solved. Moreover, increase of the amount of the flame retardant easily results in deterioration of foam formability and it tends to be difficult to obtain a satisfactory molded product.
Further, a production method for an extruded styrene resin foam excellent in environment compatibility by using a non-halogenated hydrocarbon blowing agent is disclosed in International Publication No. WO 99/33625 pamphlet. This official gazette describes a production method for an extruded styrene resin foam satisfying the thermal insulating property of the extrusion method polystyrene foam thermal insulating board Class 3a or 3b prescribed JIS A 9511 by using a hydrocarbon to make a foam flon-free and using an ether to make a foam halogenated hydrocarbon-free. However, there is no reference to any technique to meet the flame retardant property of the extrusion method polystyrene foam thermal insulating board prescribed JIS A 9511 in the case that a hydrocarbon blowing agent is used at a high ratio, and in order to increase the industrial significance, some improvement is desired.
Further, in the case of using as a blowing agent non-flon, non-halogenated hydrocarbon with poor plasticizing effect and solubility against a styrene resin, if conventional foaming conditions and production method are employed, in some cases voids are formed in a foam and molding alteration following the pressure alteration in an extrusion system occurs owing to the insufficient dissolution of the blowing agent to make stable production very difficult. Accordingly, in the industrial production of a foam, further improvement is expected in the term of productivity stability.
On the other hand, as a prior art to make it possible to provide a high thermal insulating property, methods for modifying the cell structure of a foam to a characteristic cell structure in which two types of cells, i.e. large cells and small cells coexist to improve the thermal insulating property are disclosed in JP 3-109445 A, JP 3-27304 A, JP 4-80240 A, International Publication No. WO 99/54390 pamphlet. Nevertheless, when the size of an extruder is scaled up for actualization and mass production, such characteristic cell structure cannot stably be obtained in some times and thus further improvement is required to improve the thermal insulating property and to satisfy both the thermal insulating property and the flame retardant property.
As for a foam bearing a skin layer employed for thermal insulating and water-proofing of rooftop and civil engineering, good appearance and smoothness are simultaneously required for the foam surface and therefore, technically, the difficulty is further increased and improvement of the foam forming technique is especially required.
Since a saturated hydrocarbon compound is a combustible gas, in the case that a large quantity of it is used, the flame retardant property of foam prescribed in JIS A 9511 is hard to be maintained. Further, since the thermal conductivity of the saturated hydrocarbon compound in a gas state is high as compared with flons, excellent thermal insulating property tends to be difficult to be obtained. Further, in the case of stably producing a foam using non-flon, non-halogenated hydrocarbon, practically, production technique has to be improved. Owing to these problems, no extruded styrene resin foam using a saturated hydrocarbon and provided with high-level thermal insulating property and flame-retardant property which are required for the extrusion method polystyrene foam thermal insulating board Class 3a or 3b prescribed JIS A 9511 is made industrially available and its materialization is highly expected.
Especially, this is similar in the case of a foam bearing a skin layer and materialization of an excellent foam is desired.
In view of the foregoing prior art, it is an object of the present to provide an extruded styrene resin foam with outstandingly high-level thermal insulating property and flame retardant property without using as a blowing agent flons which have effects on the environment, such as the ozone layer destruction, global warming, and the like.
Another object of the present is to provide an extruded styrene resin foam bearing a skin layer with outstandingly high-level thermal insulating property and flame retardant property without using as a blowing agent flons which have effects on the environment, such as the ozone layer destruction, global warming, and the like.
Further object of the present invention is to provide a method for stably producing an extruded styrene resin foam with outstandingly high-level thermal insulating property and flame retardant property without using as a blowing agent flons which have effects on the environment, such as the ozone layer destruction, global warming, and the like, additionally, without using halogenated hydrocarbons and the like which restrict the work environments in production of a foam and instead, using a non-halogenated blowing agent with low environmental load.